Locally advanced rectal cancer receiving total neoadjuvant therapy combined with nivolumab: a case report and literature review.

BACKGROUND: The standard treatment for locally advanced rectal cancer (LARC) is preoperative chemoradiotherapy (CRT) followed by surgery and adjuvant chemotherapy. However, it has been suggested that intensification of neoadjuvant treatment with polychemotherapy in addition to CRT instead of as an adjuvant chemotherapy is better tolerated and associated with a higher pathological complete response (pCR) rate. This concept is known as total neoadjuvant therapy (TNT). Recently, the addition of immunotherapy to preoperative CRT has been reported to be useful in LARC patients with mismatch-repair-deficiency and high levels of microsatellite instability (MSI-H), but there are no reports showing the therapeutic effect of nivolumab in combination with TNT. CASE PRESENTATION: A 23-year-old man had frequent diarrhea. Preoperative examination revealed two adenocarcinomas in the rectum. His maternal grandmother had a rectal cancer patient who developed the disease at age 70s. The larger tumor was located at the peritoneal reflection, and its anterior border close to the prostate (<1 mm); there were eight enlarged pararectal lymph nodes. Considering the size and depth of the tumor, it was judged that radical resection with sufficient margins would be difficult. Therefore, it was decided that TNT would be performed. At first, CAPOX (capecitabine and L-OHP) was administered, followed by preoperative CRT (RT:50.4 Gy and capecitabine). During this period, genetic testing diagnosed this patient as MSI-H, so additional nivolumab was administered after CRT. Colonoscopy revealed that the larger tumor was no longer detectable, so robot-assisted intersphincteric resection and bilateral lateral lymph node dissection was performed. The diagnosis of pCR was made for the larger tumor and partial response was achieved for the smaller tumor, and no lymph node metastasis was found. Major complications were not observed and the patient was discharged on the 14th day after surgery. He was followed up without adjuvant chemotherapy and is alive and recurrence-free after 9 months. CONCLUSION: A case of LARC with MSI-H was treated with TNT with nivolumab, resulting in pCR and complete radical resection. This result suggests that nivolumab in addition to TNT can be an option as a preoperative strategy for LARC with MSI-H.